The present invention relates to an air conditioner that is mounted on a vehicle to air-condition the passenger compartment.
A typical on-vehicle air conditioner sets a target temperature of air that has passed through an evaporator based on thermal load information such as the outside temperature and tho temperature of the passenger compartment. The temperature of the air that has passed through the evaporator is detected by an evaporator temperature sensor, which includes, for example, a thermistor. Based on the target temperature and the temperature detected by the evaporator temperature sensor, the displacement of a variable displacement compressor is feedback controlled.
However, if the displacement of the compressor is feedback controlled by using the temperature of air immediately after it has passed through the evaporator as an index, there are the following drawbacks. That is, due to response delay of the thermistor to temperature changes and to uneven distribution of refrigerant in the evaporator, the temperature detected by the evaporator is different from the actual temperature. This is likely to cause hunting in the displacement control of the compressor and thus makes the air conditioning less comfortable.
Accordingly, it is an objective of the present invention to provide an air conditioner that suppresses hunting in the displacement control of a variable displacement compressor.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, an air conditioner for air conditioning the interior of a compartment is provided. The air conditioner includes a variable displacement compressor, a motor controller, a detection device, a current sensor, and a controller. The compressor compresses refrigerant gas and changes the displacement. The electric motor drives the compressor. The motor controller rotates the motor at a constant reference speed. The detection device detects information related to the thermal load on the air conditioner. The current sensor detects the value of current supplied to the electric motor. The controller controls the compressor based on the detected thermal load information and the detected current value. The controller further: computes a target torque of the compressor based on the thermal load information; computes a target current value to be supplied to the electric motor in accordance with the computed target torque; and controls the displacement of the compressor such that the detected current value matches the target current value.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.